Pylosian Mint is a poison used as an ingredient in The Physician's Cure.
The Heroes of Olympus
The Blood of Olympus
In The Blood of Olympus, Frank Zhang and Piper McLean go in search of the Poison of Pylos, and Frank is able to convince the descendants of the prince of Pylos to give the plant to him. After the crew of the Argo II find the other ingredients of The Physician's Cure, Jason Grace, Leo Valdez, and Piper go to visit Asclepius, the god of medicine, and he makes The Physician's Cure for them, containing Pylosian Mint.